Energy may be transferred wirelessly between two devices from an inductive component of a transmitting device to an inductive component of a receiving device. Alternatively, energy may be transferred wirelessly from a capacitive component of a transmitting device to a capacitive component of a receiving device. For ease of discussion and not by way of limitation, energy transfer via inductive components is discussed herein.
Energy transfer occurs when the receiving device is placed in the proximity of a magnetic field generated by the transmitting device. The magnetic field at the transmitting device is generated by exciting the coil at the transmitting device with an alternating current.
Power may be described mathematically as having a real component and an imaginary component, referred to as active power and reactive power, respectively. Generally speaking, active power is either transferred to a load or dissipated in parasitic components within or in close proximity of the system, whereas reactive power is stored in the system in the form of oscillating voltages and currents in reactive elements such as inductors and capacitors.
Ideally, all active power is transferred from the transmitting device to one or more receiving devices. However, power may be lost in the transmitting device, for example to heat, or lost when power is absorbed by metal objects near the transmitting device. Further, power may be lost in the receiving device.
Many other factors affect power transfer, including distance between transmitting and receiving devices, resonant frequency of transmitting and receiving devices, frequency at which the transmitter device is excited, number of receiving devices, objects other than receiving devices near the transmitting device, size and relative size of coils, and orientation of coils, to name just a few. It is desirable to optimize power transfer and efficiency.
It would be desirable, therefore, to have the capability to dynamically adjust one or more operating parameters of a transmitting device or receiving device to adapt to changing operating conditions, component tolerances, and component parameter drift over time. It would be useful to define a metric whose value adequately indicates the power transmission efficiency and an amount of power or a relative amount of power being transferred. Such a metric may then be used in determining appropriate operating parameters to adjust.